A 3D grating is generally disposed at a light-outgoing side (i.e., a viewing side) of a display panel to constitute a 3D display device. When being used, an existing lens-type grating (which is one kind of 3D grating) is arranged such that a columnar lens thereof is obliquely disposed relative to a row and a column of pixels in the display panel. Specifically, as shown in FIG. 1, when a lens-type grating is designed and manufactured, the lens in the grating is formed of a part of a cylindrical lens (a part cut away from a cylinder along its axis direction). The lens in the grating includes sides formed of a plane 110 and a cambered surface 120, and two bottoms 130 which are perpendicular to both the plane 110 and the cambered surface 120. Wherein, the cambered surface 120 is a part of a side of the cylinder. As shown in FIG. 2 (a rectangle with reference number of 1, a rectangle with reference number of 2, and a rectangle with reference number of 3 represent viewpoint images displayed by different sub-pixels, sub-pixels with the same reference number form a complete viewpoint image; and different viewpoint images are images of the same object shot from different angles), when being used, the columnar lens of the lens-type grating is obliquely disposed. In this case, when viewed from a viewing side of a screen (the screen is perpendicular to a horizontal plane), an intersecting line between the cambered surface 120 and a section formed by the intersection of the horizontal plane and the lens is an elliptical arc. That is, the intersecting line between the cambered surface 120 and the section, which forms a predetermined angle A with an axial direction (a direction of a line connecting centers of the two bottoms 130) of the lens and is perpendicular to the plane 110 is the elliptical arc. The lens is obliquely disposed, which is equivalent to the fact that a lens with an elliptical cambered surface is arranged in front of the display panel. The lens with an elliptical cambered surface will also play the role of converging parallel light. However, focal lengths of the converging lens with an elliptical cambered surface are not uniform and a focus range is large (i.e., parallel light cannot converge at one point), which result in the fact that light output from the display panel generates a large spherical aberration after passing through the lens. As shown by the dashed oval frame in FIG. 3, light passing through the lens cannot converge at one point. The spherical aberration will increase a 3D crosstalk and further affects a 3D viewing angle to narrow down the viewing angle.